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345 lines
8.6 KiB
Groff
345 lines
8.6 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)wait.2 8.2 (Berkeley) 4/19/94
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.\" $FreeBSD$
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.\"
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.Dd November 12, 2005
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.Dt WAIT 2
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.Os
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.Sh NAME
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.Nm wait ,
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.Nm waitpid ,
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.Nm wait4 ,
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.Nm wait3
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.Nd wait for process termination
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/wait.h
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.Ft pid_t
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.Fn wait "int *status"
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.In sys/time.h
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.In sys/resource.h
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.Ft pid_t
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.Fn waitpid "pid_t wpid" "int *status" "int options"
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.Ft pid_t
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.Fn wait3 "int *status" "int options" "struct rusage *rusage"
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.Ft pid_t
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.Fn wait4 "pid_t wpid" "int *status" "int options" "struct rusage *rusage"
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.Sh DESCRIPTION
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The
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.Fn wait
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function suspends execution of its calling process until
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.Fa status
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information is available for a terminated child process,
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or a signal is received.
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On return from a successful
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.Fn wait
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call,
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the
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.Fa status
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area contains termination information about the process that exited
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as defined below.
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.Pp
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The
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.Fn wait4
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system call provides a more general interface for programs
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that need to wait for certain child processes,
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that need resource utilization statistics accumulated by child processes,
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or that require options.
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The other wait functions are implemented using
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.Fn wait4 .
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.Pp
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The
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.Fa wpid
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argument specifies the set of child processes for which to wait.
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If
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.Fa wpid
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is -1, the call waits for any child process.
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If
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.Fa wpid
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is 0,
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the call waits for any child process in the process group of the caller.
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If
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.Fa wpid
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is greater than zero, the call waits for the process with process id
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.Fa wpid .
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If
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.Fa wpid
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is less than -1, the call waits for any process whose process group id
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equals the absolute value of
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.Fa wpid .
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.Pp
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The
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.Fa status
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argument is defined below.
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The
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.Fa options
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argument contains the bitwise OR of any of the following options.
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The
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.Dv WCONTINUED
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option indicates that children of the current process that
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have continued from a job control stop, by receiving a
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.Dv SIGCONT
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signal, should also have their status reported.
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The
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.Dv WNOHANG
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option
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is used to indicate that the call should not block if
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there are no processes that wish to report status.
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If the
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.Dv WUNTRACED
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option is set,
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children of the current process that are stopped
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due to a
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.Dv SIGTTIN , SIGTTOU , SIGTSTP ,
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or
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.Dv SIGSTOP
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signal also have
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their status reported.
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.Pp
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If
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.Fa rusage
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is non-zero, a summary of the resources used by the terminated
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process and all its
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children is returned (this information is currently not available
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for stopped or continued processes).
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.Pp
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When the
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.Dv WNOHANG
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option is specified and no processes
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wish to report status,
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.Fn wait4
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returns a
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process id
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of 0.
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.Pp
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The
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.Fn waitpid
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function is identical to
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.Fn wait4
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with an
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.Fa rusage
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value of zero.
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The older
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.Fn wait3
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call is the same as
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.Fn wait4
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with a
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.Fa wpid
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value of -1.
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.Pp
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The following macros may be used to test the manner of exit of the process.
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One of the first three macros will evaluate to a non-zero (true) value:
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.Bl -tag -width Ds
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.It Fn WIFCONTINUED status
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True if the process has not terminated, and
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has continued after a job control stop.
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This macro can be true only if the wait call specified the
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.Dv WCONTINUED
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option).
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.It Fn WIFEXITED status
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True if the process terminated normally by a call to
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.Xr _exit 2
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or
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.Xr exit 3 .
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.It Fn WIFSIGNALED status
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True if the process terminated due to receipt of a signal.
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.It Fn WIFSTOPPED status
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True if the process has not terminated, but has stopped and can be restarted.
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This macro can be true only if the wait call specified the
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.Dv WUNTRACED
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option
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or if the child process is being traced (see
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.Xr ptrace 2 ) .
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.El
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.Pp
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Depending on the values of those macros, the following macros
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produce the remaining status information about the child process:
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.Bl -tag -width Ds
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.It Fn WEXITSTATUS status
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If
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.Fn WIFEXITED status
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is true, evaluates to the low-order 8 bits
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of the argument passed to
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.Xr _exit 2
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or
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.Xr exit 3
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by the child.
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.It Fn WTERMSIG status
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If
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.Fn WIFSIGNALED status
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is true, evaluates to the number of the signal
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that caused the termination of the process.
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.It Fn WCOREDUMP status
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If
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.Fn WIFSIGNALED status
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is true, evaluates as true if the termination
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of the process was accompanied by the creation of a core file
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containing an image of the process when the signal was received.
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.It Fn WSTOPSIG status
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If
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.Fn WIFSTOPPED status
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is true, evaluates to the number of the signal
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that caused the process to stop.
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.El
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.Sh NOTES
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See
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.Xr sigaction 2
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for a list of termination signals.
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A status of 0 indicates normal termination.
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.Pp
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If a parent process terminates without
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waiting for all of its child processes to terminate,
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the remaining child processes are assigned the parent
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process 1 ID (the init process ID).
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.Pp
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If a signal is caught while any of the
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.Fn wait
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calls are pending,
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the call may be interrupted or restarted when the signal-catching routine
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returns,
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depending on the options in effect for the signal;
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see discussion of
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.Dv SA_RESTART
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in
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.Xr sigaction 2 .
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.Pp
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The implementation queues one
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.Dv SIGCHLD
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signal for each child process whose
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status has changed, if
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.Fn wait
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returns because the status of a child process is available, the pending
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SIGCHLD signal associated with the process ID of the child process will
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be discarded.
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Any other pending
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.Dv SIGCHLD
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signals remain pending.
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.Pp
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If
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.Dv SIGCHLD
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is blocked,
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.Fn wait
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returns because the status of a child process is available, the pending
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.Dv SIGCHLD
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signal will be cleared unless another status of the child process
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is available.
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.Sh RETURN VALUES
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If
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.Fn wait
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returns due to a stopped, continued,
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or terminated child process, the process ID of the child
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is returned to the calling process.
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Otherwise, a value of \-1
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is returned and
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.Va errno
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is set to indicate the error.
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.Pp
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If
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.Fn wait4 ,
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.Fn wait3 ,
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or
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.Fn waitpid
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returns due to a stopped, continued,
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or terminated child process, the process ID of the child
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is returned to the calling process.
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If there are no children not previously awaited,
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-1 is returned with
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.Va errno
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set to
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.Er ECHILD .
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Otherwise, if
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.Dv WNOHANG
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is specified and there are
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no stopped, continued or exited children,
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0 is returned.
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If an error is detected or a caught signal aborts the call,
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a value of -1
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is returned and
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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The
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.Fn wait
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function
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will fail and return immediately if:
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.Bl -tag -width Er
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.It Bq Er ECHILD
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The calling process has no existing unwaited-for
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child processes.
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.It Bq Er ECHILD
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No status from the terminated child process is available
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because the calling process has asked the system to discard
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such status by ignoring the signal
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.Dv SIGCHLD
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or setting the flag
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.Dv SA_NOCLDWAIT
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for that signal.
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.It Bq Er EFAULT
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The
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.Fa status
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or
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.Fa rusage
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argument points to an illegal address.
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(May not be detected before exit of a child process.)
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.It Bq Er EINTR
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The call was interrupted by a caught signal,
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or the signal did not have the
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.Dv SA_RESTART
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flag set.
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.El
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.Sh SEE ALSO
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.Xr _exit 2 ,
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.Xr ptrace 2 ,
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.Xr sigaction 2 ,
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.Xr exit 3 ,
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.Xr siginfo 3
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.Sh STANDARDS
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The
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.Fn wait
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and
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.Fn waitpid
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functions are defined by POSIX;
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.Fn wait4
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and
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.Fn wait3
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are not specified by POSIX.
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The
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.Fn WCOREDUMP
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macro
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and the ability to restart a pending
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.Fn wait
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call are extensions to the POSIX interface.
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.Sh HISTORY
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The
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.Fn wait
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function appeared in
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.At v6 .
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